enthalpy of solu/hyd

• hydrated ions held together by ion-dipole forces
• Dissolving one mole of MgCl2

  MgCl2 (s) -> Mg2+ (aq) + 2Cl- (aq)
• • When an ionic salt is dissolved in water, the ionic lattice breaks up into ions
  • These ions interact with the polar water molecules to form hydrated ions, which are held together by ion-dipole forces
• The enthalpy of solution is the enthalpy change when 1 mol of a solute, in its standard state, dissolves in water to form aqueous ions.
• Breaking apart an ionic lattice is what kind of process?

  endothermic
• The ion-dipole attraction between ions and polar water molecules is what kind of process?

  exothermic
• Enthalpy of solution can be either endothermic or exothermic, depending on the strength of the ionic lattice that is broken and the strength of ion-dipole interactions formed.
• What do we call a reaction where gaseous ions are converted into hydrated ions?

  enthalpy change of hydration
• The enthalpy change of hydration is the enthalpy change when 1 mole of gaseous ions are converted into aqueous ions
• The direct conversion of gaseous ions to aqueous ions is impossible
• • Gaseous ions have no bonds or intermolecular forces
  • After hydration, they become aqueous ions
  • There are ion-dipole forces between the aqueous ions and polar water molecules
  • The formation of these forces is exothermic, therefore the enthalpy of hydration is always exothermic
• When ions are in their gaseous state, they have

  • no bonds
  • no intermolecular forces
• The factors that determine the strength of attraction between ions and polar water molecules are:

  • The magnitude of an ion’s charge
  • The size of an ion
• The enthalpy of hydration will always be exothermic
• The two factors that will lead to a more exothermic enthalpy of formation are

  • smaller ion size
  • greater ion charge